The β‐1,3‐glucanosyltransferases (Gels) affect the structure of the rice blast fungal cell wall during appressorium‐mediated plant infection

• Published in: Cellular microbiology Vol. 19; no. 3; pp. np - n/a
• Main Authors: Samalova, Marketa, Mélida, Hugo, Vilaplana, Francisco, Bulone, Vincent, Soanes, Darren M., Talbot, Nicholas J., Gurr, Sarah J.
• Format: Journal Article
• Language: English
• Published: England John Wiley and Sons Inc 01.03.2017
• Subjects: beta-Glucans - analysis; Cell Wall - chemistry; Editor's Choice; Gene Deletion; Glucan Endo-1,3-beta-D-Glucosidase - genetics; Glucan Endo-1,3-beta-D-Glucosidase - metabolism; Magnaporthe - enzymology; Magnaporthe - genetics; Magnaporthe - metabolism; Magnaporthe - pathogenicity; Oryza - microbiology; Plant Diseases - microbiology; Spores, Fungal - enzymology; Spores, Fungal - metabolism
• ISSN: 1462-5814; 1462-5822; 1462-5822
• DOI: 10.1111/cmi.12659

The fungal wall is pivotal for cell shape and function, and in interfacial protection during host infection and environmental challenge. Here, we provide the first description of the carbohydrate composition and structure of the cell wall of the rice blast fungus Magnaporthe oryzae. We focus on the family of glucan elongation proteins (Gels) and characterize five putative β‐1,3‐glucan glucanosyltransferases that each carry the Glycoside Hydrolase 72 signature. We generated targeted deletion mutants of all Gel isoforms, that is, the GH72+, which carry a putative carbohydrate‐binding module, and the GH72− Gels, without this motif. We reveal that M. oryzae GH72+ GELs are expressed in spores and during both infective and vegetative growth, but each individual Gel enzymes are dispensable for pathogenicity. Further, we demonstrated that a Δgel1Δgel3Δgel4 null mutant has a modified cell wall in which 1,3‐glucans have a higher degree of polymerization and are less branched than the wild‐type strain. The mutant showed significant differences in global patterns of gene expression, a hyper‐branching phenotype and no sporulation, and thus was unable to cause rice blast lesions (except via wounded tissues). We conclude that Gel proteins play significant roles in structural modification of the fungal cell wall during appressorium‐mediated plant infection. The fungal cell wall is pivotal for cell protection, determination of cell shape and function and during host infection. This paper details the carbohydrate composition of the rice blast fungus cell wall and analysis of a family of β‐1,3‐glucan glucanosyltransferases (Gels) during infective and vegetative growth. Gel proteins are expressed during infection‐related development and plant infection, and a null mutant Δgel1Δgel3Δgel4, with modified cell wall 1,3‐glucans shows a hyper‐branching phenotype with no sporulation, and is thus non‐pathogenic.